1. Field of the Invention
The present invention relates to a data transmission device and, more particularly, to a data transmission device which can be attached to a magnetic recording and reproducing apparatus performing a data recording or reproducing operation on a recording medium by using a magnetic recording and reproducing head, a memory medium being accommodated in the data transmission device so that a recording or reproducing operation on the memory medium is performed via the magnetic recording and reproducing apparatus, the memory medium having memory elements for storing information therein.
2. Description of the Related Art
A memory card is popular as a memory mainly for portable computers such as a notebook-type PC (personal computer). In association with downsizing of PCs and popularization of digital cameras, a small memory card has become popular in the market.
There are several types of small memory cards such as a miniature card type or a smart media type, and small memory cards having a memory capacity of 2 MB to 8 MB have come into a wide use in the market. Recently, an IC card having a memory capacity for storing a relatively small amount of data such as individual information or identification information (ID) has become popular.
However, in order to store information in such a small-type memory card or an IC card, a recording and reproducing apparatus exclusive for each medium is required. Accordingly, such an exclusive recording and reproducing apparatus must be connected to a conventional personal computer when the memory card is used with the conventional personal computer. Additionally, a space must be reserved inside the personal computer when the exclusive recording and reproducing apparatus is incorporated into the personal computer.
This is contrary to a trend of downsizing of the personal computer. Accordingly, it is suggested that a method for using a floppy disc drive as a recording and reproducing apparatus be used for recording or reproducing the IC card since the floppy disc drive is popular in the personal computer market and is incorporated in most personal computers as a data storing medium.
The basic concept of such a technology to permit usage of the small-type memory card or the IC card by the floppy disc drive is that no change should be made to the conventional floppy disc drive. That is, considering the popularization of the floppy disc drive on the market, the use of the conventional floppy disc drive has an advantage. Accordingly, a method has been developed in which the small-type memory card or the IC card is attached to an adapter having an outside configuration similar to the floppy disc cartridge so that the adapter is attached to the floppy disc drive, and, thereby, the memory card or the IC card is magnetically connected to the floppy disc drive via a magnetic head of the floppy disc drive so as to exchange signals therebetween.
FIG. 1 is a block diagram of a conventional floppy disc drive.
A floppy disc 2 is inserted into the floppy disc drive 1. A slide shutter 4 of the floppy disc 2 is opened by a loading mechanism 3 during an insertion of the floppy disc 2, and, thereby, a magnetic head 6 contacts a disc 5 accommodated in the floppy disc 2.
When the floppy disc 2 is loaded at a predetermined loading position inside the floppy disc drive 1, a spindle motor 7 is engaged with the disc 5. The disc 5 is rotated by the spindle motor 7 in a direction indicated by an arrow A at a predetermined speed, and the magnetic head 6 slides on the disc 5 so that data is recorded by magnetizing the disc 5 by the magnetic head 6.
The magnetic head 6 is mounted on an actuator 8, and is moved in a radial direction (direction of an arrow B) of the disc 5. Data is recorded on the disc 5 by moving the magnetic head 6 in a radial direction (direction of the arrow B) by operating the actuator 8.
The spindle motor 7 is connected to a motor control circuit 9 so as to be rotated at a constant rotational speed. The motor control circuit 9 is connected to a control circuit 10 so as to control an operation of the spindle motor 7 in response to a motor control signal provided from the control circuit 10.
The actuator 8 is connected to the control circuit 10. The actuator 8 moves the magnetic head 6 in a radial direction (direction of the arrow B) of the disc 5 in response to a tracking position control signal so as to select a tracking position.
Additionally, the magnetic head 6 is connected to a read/write circuit 11 so as to record data on the disc 5 by a recording signal provided from the read/write circuit 11. The magnetic head 6 also detects information recorded on the disc 5 by converting changes in magnetization of the disc 5 into a current. The read/write circuit 11 amplifies write data and provides the amplified write data to the magnetic head 6. The read/write circuit also restores an original signal by processing read signals.
A description will now be given, with reference to FIG. 2, of the read/write circuit 11.
FIG. 2 is a block diagram of the read/write circuit 11 of the conventional floppy disc drive 1.
The read/write circuit 11 comprises a flip-flop 21 which hold the write data; a write amplifier 22 which amplifies the data held by the flip-flop 21; a preamplifier 23 which amplifies read signals detected by the magnetic head 6; a low-pass filter 24 which cuts off a high-frequency component of read signals amplified by the per-amplifier 23; a differentiating circuit 25 which differentiates the read signals output from the low-pass filter 24; a zero-cross comparator 26 which detects a zero-crossing point of the differentiated signal output from the differentiating circuit 25; and a waveform shaping circuit 27 which shapes an output waveform of the zero-crossing comparator 26. The waveform shaping circuit 27 includes a time domain filter (TDF) 25 which removes a noise component from the output signal of the zero-cross comparator 26.
A description will now be given, with reference to FIG. 3, of an operation of the read/write circuit 11.
FIG. 3 is a waveform chart of an operation of the read/write circuit of the conventional floppy disc drive. FIG. 3-(A) shows the write data provided to the flip-flop 21; FIG. 3-(B) shows output data of the flip-flop 21; FIG. 3-(C) shows a head write current; FIG. 3-(D) shows a state of magnetization of the disc 5; FIG. 3-(E)shows a head read voltage detected by the magnetic head 6; FIG. 3(F) is an output of the differentiating circuit 25; FIG. 3(G) shows an output of the comparator 26; and FIG. 3-(H) is an output of the waveform shaping circuit 27.
The write data shown in FIG. 3-(A) is held by the flip-flop 21 as shown in FIG. 3-(B), and is converted into a waveform which can easily magnetize the disc 5. The signal shown in FIG. 3-(B) is provided to the magnetic head 6 as a write signal which has a waveform as shown in FIG. 3-(D) so as to magnetize the disc 5. It should be noted that the disc 5 is magnetized as shown in FIG. 3-(D) by the waveform shown in FIG. 3-(C).
When a magnetization pattern shown in FIG. 3-(D) is scanned by the magnetic head 6, a voltage shown in FIG. 3-(E) is obtained. At this time, the magnetic head 6 generates a current at positions where the magnetization is changed. The read voltage of the magnetic head 6 is influenced by a state of the immediately preceding magnetization, and shows relatively gentle changes as shown in FIG. 3-(E). The read voltage generated by the magnetic head 6 is differentiated by the differentiating circuit 25, and the signal shown in FIG. 3-(F) is obtained. At this time, since the read voltage generated by the magnetic head 6 gently changes as shown in FIG. 3-(E), the signal obtained by the differentiation has relatively small flat portions as shown in FIG. 3-(F).
The signal shown in FIG. 3-(F) is subjected to a detection of a zero-crossing point by the zero-crossing comparator 26, and a waveform shown in FIG. 3-(G) is obtained. This waveform corresponds to a result of detection of peaks in the read voltage shown in FIG. 3-(E). That is, pulses which reverse at positions where the magnetization of the disc 5 is changed are detected.
By generating pulses at reversed positions of the output of the comparator 26, an original signal shown in FIG. 3-(A) is restored as shown in FIG. 3-(H).
The above-mentioned modulation method is referred to as a Modified Frequency Modulation (MFM) method, and is generally used for the conventional floppy disc.
In such a modulation method, a resolution of data reproduction greatly influences a reading operation of data recorded on the disc 5. For example, when a plurality of pulses are read, a solitary wave is obtained by a combination of a positive polarity and a negative polarity which combination corresponds to a reverse in the magnetization on the disc 5. At this time, if adjacent solitary waves are too separate from each other or too close to each other, a degree of change in a root of the solitary wave in the read voltage shown in FIG. 3-(E) is reduced. The root of the solitary wave is referred to as a shoulder which is indicated by a dashed circle in FIG. 3(E). When the signal having a shoulder which has less change is differentiated, a saddle noise is generated in the shoulder as indicated by a dashed circle in FIG. 3-(F). If the saddle noise crosses a reference level (OV), the zero-crossing comparator 26 detects the saddle noise which may result in generation of a pulse which is not present in the original signal. Especially, since a floppy disc is rotated at a constant speed in the floppy disc drive, recording density differs from an inner side to an outer side of the disc, and, thereby, the shoulder is elongated in the outer side of the floppy disc. Accordingly, the above-mentioned influence of the saddle noise is increased in the outer side of the floppy disc.
In order to solve the above-mentioned problem in the floppy disc drive, the saddle noise is removed by using the time domain filter (TDF) 28 or the resolution is adjusted to fall within an optimum range by changing a read filter between the inner side and the outer side of the disc.
A description will now be given of a case in which information is recorded on or reproduced from the memory card (IC card) by the floppy disc drive.
FIG. 4 is a block diagram of a structure for providing data via the magnetic head of the conventional floppy disc drive. In FIG. 4, parts that are the same as the parts shown in FIG. 2 are given the same reference numerals, and descriptions thereof will be omitted.
When information is recorded on or reproduced from the memory card (IC card), the magnetic head 6 of the floppy disc drive 1 is contacted by a magnetic head core 31 so as to magnetically input and output information. In this case, an output of the IC card includes square waves, and the square waves are provided to the magnetic head 6 of the floppy disc drive.
FIG. 5 is a waveform chart of an operation for providing data via the magnetic head of the conventional floppy disc. FIG. 5-(A) shows data provided to the magnetic head core 31; FIG. 5-(B) shows a read voltage of the magnetic head 6; and FIG. 5-(C) shows an output waveform of the differentiating circuit 25.
When the data shown in FIG. 5-(A) is directly provided to the magnetic head core 31 so as to read the data by the magnetic head 6 of the floppy disc drive 1, a differentiated waveform having a peak corresponding to the reverse in the data is generated as shown in FIG. 5-(B) since the magnetic head 6 detects the reverse in the data. In such a case, the change corresponding to the reverse in the data is faster than that of the signal obtained by reading information on the floppy disc 5 as shown in FIG. 3-(E). Accordingly, there is no change in output at a flat portion, that is, the shoulder, which results in generation of the saddle noise.
Additionally, when an IC card is read by the conventional floppy disc drive 1, a reading speed should be constant and the floppy disc drive 1 should be used without changes in an arrangement, since a compensation for data peculiar to the IC card cannot be made by the floppy disc drive 1.
However, when data is read from an IC card by a floppy disc drive using the conventional Modified Frequency Modulation (MFM) method, data output from the IC card has a waveform having a steep peak at a reverse of the data. Accordingly, the read voltage read by the magnetic head of the floppy disc drive has a waveform in which sharp changes occur at the reverse in the data as shown in FIG. 5-(B) and a degree of change at the shoulder is decreased. When such a waveform is differentiated, a saddle noise is generated at the shoulder. If the saddle noise crosses a reference level (0V), such a crossing is detected by the zero-crossing comparator 26. Accordingly, there is a problem in that a pulse which is not present in the original data is generated and such a pulse causes an error in reading the data.